Abstract
Methyl 2,3-butadienoate (1) undergoes EtAlCl2-catalyzed stereospecific [2 + 2] cycloadditions with alkenes to give methyl cyclobutylideneacetates in good yield. The stereospecificity and ratios of E and Z isomers suggest a [,2, + ,2a] cycloaddition of the l-EtA!Cl2 complex analogous to that of ketenes.